The present invention relates to an engine cover to be employed in an automobile or the like, and more particularly to a structure of the engine cover in which noises can be further decreased.
Recently, in an engine room of an automobile, it has been customary that an engine cover is provided in an upper part of a cylinder head cover of an engine. This engine cover is formed of thermoplastic resin or the like into a plate-like shape, and provided with ornamental characters or patterns which have been drawn on its surface with light tone of warm colors, so that its aesthetic appearance may be enhanced.
It is also required for the engine cover to insulate sounds emitted from the engine so as to decrease noises leaking from the engine room. For this purpose, there has been employed an engine cover composed of a hard cover body and a layer of sound absorbing member which is stacked to a surface of the cover body opposed to the engine. By attaching the sound absorbing member layer in this manner, the sound absorbing member layer absorbs the sounds emitted from the engine. Accordingly, leak of the sounds to an exterior of the automobile can be more effectively restrained owing to synergistic effect between sound absorption by the sound absorbing member layer and sound insulation by the cover body.
As the sound absorbing member to be employed in such the sound absorbing layer, there have been known fiber type sound absorbing members such as non-woven fabrics of synthetic resin formed of PET or the like, non-woven fabrics made of natural fibers, glass wool laminates, etc., or alternatively, foam type sound absorbing members such as urethane foam, foamed olefin, etc.
However, when the noises have been measured at a position apart from a surface of the engine cover by a determined distance, it has been found that due to provision of the engine cover, sound pressure levels of the noises in a relatively low sound range having frequencies of about 300 to 800 Hz have been rather increased. Sufficient absorption of the noises in such a frequency range is difficult with the sound absorbing member layer which has been heretofore employed.
It is considered that this phenomenon is due to resonance occurring in a somewhat closed space which is formed between the engine cover and engine members.
The present invention has been made in view of such circumstances as described above, and an object of the present invention is to decrease noises from an engine all the more, by further decreasing resonant sounds.
A feature of an engine cover according to the present invention for solving the above described problem lies in the engine cover held by engine members, characterized in that the engine cover comprises a cover body in a plate-like shape and a sound absorbing member layer stacked to a surface on a back face side of the cover body, the cover body including a through hole penetrating both sides of the cover body in an area opposed to a resonant space which is formed between the cover body and the engine members, and in which resonant sounds are generated, wherein an opening of the through hole on the back face side of the cover body is covered with the sound absorbing member layer.
This sound absorbing member layer has preferably air permeability.
Moreover, it is desirable that an opening area of the through hole is 100 mm2 or more, and an opening rate of the through hole is 45% or less.